(CNSNews.com) - Conservative talk-show host Mark Levin says Congress should have looked deeper into reports that the Internal Revenue Service was targeting conservative groups a year ago, "before the election cycle ran out."

Levin told Fox News's Sean Hannity Monday night that one of the most troubling issues about the IRS political witch-hunt is "the passivity and timidity of Congress."

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"The fact is, a year ago Congress should have been calling witnesses before their committees, should have placed them under oath, should have been pursuing possible perjury claims and should have gotten to the bottom of this before the election cycle ran out.

"Why, for the life of me, these committee chairman now are beating their chests and they're talking about their hearings they will conduct, why for the life of me they didn't do this a year ago is very troubling."

Levin said he believes Republicans in Congress dismissed reports that the IRS was harrassing conservatives because "it involved the Tea Party." He noted that the GOP is "no great cheerleader for the Tea Party and other conservative groups."

"And so, they were relatively dismissive. They fired off a few letters, they asked a few questions but they didn't really conduct an aggressive focused investigation to get to the bottom of this."

Levin said the IRS developed an "enemy's list" with only one enemy on it -- conservatives in general and the Tea Party in particular.. Chairman (Dave) Camp (R-Mich.), I believe his name is, of the House Ways and Means Committee put out a statement today about this hearing they are going to have on Friday. And it's very genetic, very bureaucratic. They will look into politically partisan activities of the IRS. This isn't about politically partisan activities by the IRS. This is about an attack on the Tea Party and the conservative movement."

Levin said what Congress needs to investigate is "exactly what the IRS just confessed to, which is targeting conservatives and Tea Party groups, not the generic watered-down, 'We're going to see if the IRS was partisan.' I can answer that under oath -- yes, they were partisan. Now find out exactly what they did."

Levin said Congress has an "Article I responsibility" to "get information under oath" from IRS agents and their bosses "on what the IRS has already confessed to, and see if it broadens out from there."

The same duty applies to other cases of "big government tyranny," Levin said:

"Folks, it's real world. The IRS is out of control, the Department of HHS with Obamacare is out of control. The Agriculture Department with the scandal, with the payoffs to different groups, is completely out of control. The Interior Department and oil drilling -- the government is big, it's bloated, it's getting more and more powerful -- and if you believe in liberty, you better start paying attention.

"The Congress has a job and they better do it," he said.

Levin's Landmark Legal Foundation filed a complaint a year ago, in March 2012, about the IRS tactics, requesting that the Treasury Department's Inspector General for Tax Administration to investigate the matter, which it did.

As CNSNews.com reported, the IG has provided a timeline to congressional staff indicating that in the 2010 election year, the IRS instructed officials in its "Determinations Unit" to "be on the lookout for" organizations applying for tax-exempt status that used the words "tea party" or "patriot" in their applications.

By January 2012, at the beginning of a presidential election year, according to the timeline, the IRS broadened its "be on the lookout order" to target groups that were involved in educating people on the Constitution and the Bill of Rights.

Lois Lerner, director of the IRS Exempt Organizations Division, admitted at an American Bar Association conference last week that the IRS had targeted for special review applications of non-profit groups that included the words “tea party” or “patriot.”

“That was wrong,” the AP quoted Lerner as saying. “That was absolutely incorrect, it was insensitive and inappropriate. That’s not how we go about selecting cases for further review.”